fix(catalog): let the variables panel actually drive the composition

Every control on the panel was inert. The values reached the composition and
nothing repainted, because the payload had already been compiled: compiling
inlines a mounted component and resolves its variables into the markup and CSS,
so by the time a reader turns a knob there is nothing left to change.

An item that declares variables now ships uncompiled, keeping the mount the
runtime loads at run time, which is the only state where data-variable-values
still means anything. The component travels inline as a data URI rather than a
sibling file, because .html is the one type the docs host will not publish. The
demo's own pinned values come off, so the reader's choices reach the mount
instead of losing to the values the demo picked to show itself off.

Measured on the rendered frame rather than the DOM: green rgb(98,207,144),
blue rgb(6,6,199), violet rgb(177,147,230), and back to green.

docs/public/catalog drops from 48 MB to 35 MB along the way, since an
uncompiled payload carries far less than an inlined one.

Author: miguel-heygen